Kevin Mitchell is a cousin of Keith Mitchell. He grew up in a tough neighborhood of San Diego, CA where he was allegedly involved with street gangs and shot at a few times. Still, he could play baseball and was signed by the New York Mets as an amateur free agent in 1980.

Mitchell has had a history of behavioral problems. In Dwight Gooden's autobiography it was claimed that Mitchell held Gooden hostage and killed his cat. Mitchell has always denied the story. In 1999, he was arrested for assaulting his father during an argument. Playing in the independent Western Baseball League in 2000, he was suspended for punching the owner of a rival team in the mouth during a brawl. On April 4, 2011, he was sentenced to three years' probation after pleading guilty to attacking a man on a golf course in Bonita, CA. He has also been in trouble with the IRS for a huge amount of unpaid back taxes. A number of other stories circulate about him, although they are not well-referenced.

He started his career as a super-sub in his rookie season with the New York Mets when they won the World Championship in 1986. He hit .277/.344/.366 in 108 games with 22 doubles and 12 homers, playing 6 different positions. He was then acquired by the San Diego Padres in the eight-player blockbuster trade that sent Kevin McReynolds to New York after that season. It was claimed that the Mets thought he was a bad influence on young stars Gooden and Darryl Strawberry. Midway through 1987, he was involved in a second blockbuster deal, this one involving 7 players, that sent him to the Giants along with pitchers Dave Dravecky and Craig Lefferts on July 5. After hitting .246 as the starting third baseman for the Padres, he came alive in San Francisco, batting .306 and slugging .530 and the re-tooled Giants won the NL West title but fell to the St. Louis Cardinals in 7 games in the NLCS. After a solid season in 1988, when he split his time between third base and left field, Mitchell bloomed in 1989 as a full-time left fielder, leading the National League in homers (47) and RBI (125), as well as slugging percentage, OPS and OPS+. He made the most famous play of his career early that season, catching a fly ball off the bat of the Cardinals'Ozzie Smith with his bare right hand after overrunning the ball, then crashing into the wall and through an unlatched door leading under the stands at Busch Stadium, holding onto the ball all the while. That year, he had 31 home runs at the All-Star break, before slowing down somewhat in the second half of the season. The Giants beat the Chicago Cubs in the NLCS - Mitchell hit .353 with 2 homers, but was outshined by teammate Will Clark who had a monster series - then were swept by the cross-bay Oakland Athletics in the 1989 World Series. Mitchell was one of the few Giants hitters to do all right against the A's pitching, hitting .294 with a homer and 2 RBI.

Mitchell had another good season in 1990, hitting 35 homers and driving in 93 in 140 games for the Giants, but he caught the injury bug starting in 1991. He played only 113 games that season, batting .256 with 27 homers, and would never play in 100 games in a season after that. He was involved in another major trade after the season, heading to the Seattle Mariners with Mike Remlinger in return for pitchers Dave Burba, Mike Jackson and Bill Swift. The Mariners clearly lost that trade, as all three pitchers did well for their new team, while Mitchell was limited to 99 games and 9 homers and Remlinger did not emerge as a solid pitcher for a number of years. Mitchell also developed a reputation for being surly and prone to bouts of violent anger in those days, and his frequent absences from the field were often considered to be malingering, while his unwillingness to keep himself in playing shape also soured his relations with management wherever he went.

The disappointed Mariners sent Mitchell away after the 1992 season, unloading him on the Cincinnati Reds in return for reliever Norm Charlton. He found his power stroke again in Cincinnati, putting up a tremendous batting line of .353/.385/.601 in 1993, but in only 93 games. He was healthy for a change in 1994, batting .326/.429/.681 with 30 homers in 95 games, but it was the 1994 strike that cut his season short. He became a free agent after the season, and decided to sign with the Fukuoka Daiei Hawks of Nippon Pro Baseball in 1995. He hit a grand slam off Taigen Kaku in his first NPB at-bat; only one player had ever done so previously. He left the team in May, against management wishes, in order to undergo treatment for a knee injury. He returned briefly but was shut down when his knees again became a problem. In 37 games for Daiei, he hit .300/.389/.531 with 8 homers and 28 RBI in 37 games. Fans called him a "paycheck thief" as he was paid 400 million yen for those 37 games.

He signed with the Boston Red Sox in 1996 and hit .304 in 27 games with little power before the Reds re-acquired him in a minor league deal at the trading deadline. He played 37 games in August and September, hitting .325 and slugging .579, but his inability to play defense meant that the Reds cut off their ties with the aging slugger.

Mitchell tried another comeback with the Cleveland Indians in 1997 but was released in early June having batted only .153 in 20 games. He returned to the majors with the Oakland Athletics in 1998 and played his last 51 games in the majors, hitting .228. Since he could no longer run or play defense, this was not enough to justify a job and he was released for the last time on August 7. He tried to revive his career in the Independent Leagues after that, but never made it back. He also managed the Sonoma County Crushers in the Western League in 2002, going 49-41 and finishing second in their division.

Overall, in 13 major league seasons, he hit .284/.360/.520, with 224 doubles and 234 homers. Had he stayed healthy and kept himself in shape to play defense, he could conceivably have had a Hall of Fame career, as the hitting talent was always there. But his character flaws eventually got the best of him.

In 2008, Mitchell was diagnosed with diabetes and claimed the experience changed his life, as it forced him to focus on the good he could do with his life. He began to work with troubled inner-city kids, working with a non-profit foundation called "Athletes for Education". However, he did relapse into violent behavior even after finding this more meaningful occupation.